Hydraulic machine circuit



Dec. 23, 1941. w. ERNST Em 2 267 4 HYDRAULIC MACHINE CIRCUIT Filed July 1, 1937 2 Sheets-Sheet l INVENTORS WALTER ERNsT 5y 'WARREN If. TUCKER A T TORNEYS Dec, 23, 1941.

W. ERNST ET AL HYDRAULIC MACHINE CIRCUIT Filed July 1, 1937 2 Sheets-Sheet 2 /NVENTOR$ WA 1. TE? E R/vs T WARREN If. Tug 5, 4 QM ,7: 6%

ATTORNEYG Patented Dec. 23, 1941 HYDRAULIC MACHINE CIRCUIT Walter Ernst and Warren R. Tucker, Mount Gilead, Ohio, assignors to The Hydraulic Press Corn, Inc., Wilmington, Del., a corporation of Delaware Application July 1, 1937, Serial No. 151,469

6 Claims.

This invention relates to hydraulic machine circuits, and in particular, to circuits for operating hydraulic machines having multiple cylinders and pistons, and is a variation of the hydraulic system disclosed in our copending application, Serial No. 151,470, which matured to Patent No. 2,211,370.

One object of this invention is to provide a hydraulic machine circuit for operating a hydraulic machine having one cylinder to which pressure is supplied, and then held constant while pressure is supplied to another cylinder. I Another object is to provide a hydraulic machine circuit, wherein two hydraulic cylinders are operated from cooperating constant delivery and variable delivery pumps in such a manner that one of the pumps is caused to idle at substantially zero pressure when it is not needed for supplying pressure fluid.

Another object is to provide a hydraulic machine circuit having a pair of cylinder and piston assemblies operated by a pair of pumps, means being provided to unload one of the pumps when the pistons are in their retracted positions, such as when the machine is at rest.

Another object is to provide a hydraulic machine circuit, wherein two pumps are caused to .cooperate and supply pressure fluid to two hyto be unloaded, or substantially unloaded, when the low pressure pump has performed its desired functions.

In the drawings:

Figure 1 is a diagrammatic view of a hydraulic machine circuit according to one form of the invention, wherein two hydraulic motors are operated from two different pumps, both pistons of the motors being retracted simultaneously.

Figure 2 is a view similar to Figure 1, but of a slightly modified circuit in which one of the pistons may be retracted independently of the other.

General arrangement In general, the hydraulic machine circuits of enabling the operation of two independent rams or motors from a pair of high and low pressure pumps, wherein the high pressure pump always unloads, or substantially unloads, the low pressure pump when the latter has performed its work. Hitherto, attempts to do this have been circuit of Figure 1 a low pressure constant de-' livery pump and a high pressure variable delivery pump supply fluid to two independent hydraulic cylinders, the purpose of the variable pump being to maintain pressure upon one of the cylinders while the other cylinder is operated. This circuit causes the cylinder to which pressure fluid is first supplied to be held at constant pressure while pressure fluid is supplied to the second cylinder. In this circuit, however, both cylinders are retracted simultaneously, and the low pressure constant delivery pump is unloaded when both hydraulic cylinders are in their retracted position, namely, when the machine is standing open and idling. After one of the cylinders causes its piston to advance to its forward position, the circuit causes the constant delivery pump again to unload. The modified circuit shown in Figure2 enables the second cylinder to be reversed before l: reversing the first cylinder, although the constant shown in the two diagrams have the same purpose 55 delivery pump is not quite fully unloaded when the machine is at rest.

Circuit simultaneously retracting both pistons the line 20, which terminates at one end in the port 2| of the firstoperating valve, generally designated 22. The variable delivery pump l3 discharges directly into the line 20, and hence, both pumps II and I3 cooperate to supply pressure fluid to the port 2| of the first operating valve 22. valve.

The high pressure variable delivery pump I3 is of a conventional type, such as a radial piston type, wherein the eccentricity of the piston actuating ring may be varied relatively to the cylinder barrel; and thereby vary the strokes of the pistons to increase or reduce the output of the pump. This variable delivery pump I3 is provided with a control mechanism, of a type known to those skilled in the art, and forming no part of the present invention. According to the arrangement shown, a servomotor I3 has therein a piston (not shown) connected to the pump flowcontrol member or shift ring so as to shift the latter to a neutral or zero stroke position, and overcome the opposing urge of a coil spring within the spring casing I3 thereby serving to maintain pressure in the circuit when this pressure is built up to a predetermined value. The thrust of the spring and hence the said predetermined pressure may be adjusted by turning the hand wheel iii. A pump control of this type is disclosed in the Ernst Patent No. 2,039,893, issued May 5, 1936. The low pressure constant delivery pump as may likewise be of any suitable conventional type. such as the gear or vane type, and its details iorm no part oi the present invention.

The pressure relief valve Iii-is of a conventional type, and a complete disclosure thereof will be found in the Ernst Patent No. 2,086,295 of July 6, 1937. The relief valve I6 is provided with a plunger 23, urged in a downward direction This is a conventional tour-way piston by the spring 24 within the screw cap 25. Theplunger 23 contains a drilled passageway 25 interconnecting-the main valve chamber 21 and the plunger-lifting chamber 28, the flow being adjustable by means of a needle valve 23. The plunger 23 within the plunger-lifting chamber 28 is provided with an annular shoulder 30, which serves as a piston area to lift the plunger 23 when the pressure exceeds a predetermined amount, as determined by the force of the spring 24. When this amount is exceeded and the pressure lifts the plunger 23, the fluid from the constant delivery pump I4 passes from the plunger-lifting chamber 21 downwardly, through the pipe 3i, into the tank Ill.

The first operating valve 22 consists of a longitudinally bored casing 32 having a valve rod 33 with twin spaced heads 34 and 35 thereon. These heads open into spaced chambers 35, 31, 38, 39 and 40. The chambers 35 and 40 open into the ports II and 42, connected by the line 43 to the tank It. The chamber 38 opens into the port 2i and line 20, previously described. The chambers 31 and 39 open into the ports 44 and 45, to which are attached the lines 48 and 4], respectively. The line 41 leads to the port 48 in the main hydraulic cylinder 59. The latter has a piston 50 with a head I reciprocating therein. The line- 46 is connected to the port 52 at the right-hand end of the cylinder 49, and is likewise connected to the port 53 at the left-hand end of the auxiliary cylinder 54. The latter is provided with a piston 55 having a head 56.

The opposite end of th'e cylinder '54 is provided with a port 5! connected by the line 58 to the port 59 of the second operating valve, generally designated 60. The latter is of a similar construction to the first operating valve 22, and its corresponding parts bear similar numerals. The outlet ports, however, are differently designated for purposes of clarity. From the end ports 6| v-alve l8 and the pressure relief valve I6. From the remaining port 55 the line 61 runs to the port 68 of the pilot-operated unloading valve, generally designated 69. The latter is provided with a valve chamber I0 and a plunger-lifting chamber II, having pressure fluid supplied thereto by the pilot line it leading from the pressure line 20 of the high pressure variable delivery pumpi3.

The unloading valve 59 contains a plunger 73 I having an annular shoulder ill forming a piston area within the plunger-lifting chamber H, and urged downwardly by the coil spring '15 within the casing it. From the remaining port ll of the main valve chamber It the line it runs downwardly to the tank Iii. The pressures at which the pressure relief valve It and unloading valve 63 open may be adjusted by turning the screw caps 79 and 80, with which these valves are equipped.

In the operation of the hydraulic machine circuit shown in Figure l, the pumps 63 and i i are started in operation, and take in fluid through their suction lines II and I2, respectively. At the outset it will be assumed that the pistons 5t and 55 are nearing the ends of their retraction strokes, so'that the machine is approaching its position of rest. The constant delivery pump M discharges its fluid through the line l5, the pressure relief valve It, the line H, the ball check valve I8 and the lines I9 and 20, into the first operating valve 22 at the port 2i. Pressure fluid also passes from the line H, through the line 65, the second operating valve 60 and the line 61, into the valve chamber ill of the unloading valve 63. The latter, however, is closed at this stage of the operation, hence, the pressure fluid cannot yet escape. The fluid reaching the first operating valve 22 passes outwardly, through the port 44 and line 46 to the ports 52 and 53 on the pull-back sides of the cylinder 43 and 56, thereby simultaneously retracting the two pistons 5t and 55. As the pistons are nearing their retracted positions but a slight pressure will exist in the system.

When the piston heads 5i and 56 have reached the ends of their return strokes and halted, pressure will build up in the lines previously mentioned, causing a similar pressure to accumulate in the pilot line 12 and plunger-lifting chamber H of the unloading valve 69. When this becomes of a predetermined amount, it lifts the valve plunger I3 and opens communication between the main valve chamber ill and the line 18, thereby permitting the fluid therein to escape back into the tank I0. This permits the low pressure constant delivery pump it to by-pass its flow through the line Hi, the relief valve It, the lines ll and 65, the second operating valve 60, the line 61, the unloading valve 69 and the line I8, into the tank III. The high pressure variable delivery pump meanwhile discharges its fluid through the line 20, and pressure backing up in the line I3 closes the check valve I8. This pressure continues to rise until the control mech-* anism of. the high pressure variable delivery pump I3 has reached its critical pressure for which it is set, whereupon the flow-control member of the pump is shifted automatically into its neutral delivery position, in accordance with the well known principles of such pumps. The variable delivery pump I3, therefore, continues to pressure constant delivery pump I4 is being bypassed dr unloaded.

With the system at rest, therefore, and with both piston heads 5| and 56 retracted, as the pump ll is being by-passed at substantially zero pressure and pump I3 is maintaining the pressure in the system at a substantially zero stroke,

the machine is idling with its minimum power consumption. In this position the machine is in readiness for performing a subsequent working stroke. To perform a working stroke, the operator shifts the first operating valve 22 into the position opposite from that shown in-the drawings. When this is done the pull-back line 46 will be connected through the valve 22 to the discharge line 43 so that fluid can escape back into the tank I 0. The line 41, however,-will be connected to the pressure lines I! and 20, supplying pressure from the pumps ll and I3, respectively. Under these conditions, the pressure in the line 20 will drop, likewise causing the pressure in the line I2 to drop, and permitting the spring to close the plunger 13 of the unloading valve 59. i

As the low pressure pump ll can no longer bypass its discharge through the unloading valve 89, in the manner previously described, it now supplies its pressure fluid through the line I! to the line 20, which is already receiving pressure 2,267,644 I maintain pressure on the circuit while the low I fluid from the high pressure variable delivery pump 13. The pressure fluid thus received in the line 41 from both pumps [3 and ll, acts against the piston head 5| and moves the piston to the right upon its forward stroke. If the piston 50 is employed, for example, as a clamping piston for molding dies, the piston 50 now closes the dies and, clamps them. This causes pressure to be built up in the line 41 and continued backward through the valve 22, the line 20 and pilot line 12 to the unloading valve 69,

' thereby opening the latter and again bypassin the discharge of the low pressure constant delivery pump l4, in the manner previously described. At this stage the piston 5|! has reached the end of its forward stroke and is under pressure, but the piston is still in a retracted line 58, into the right-hand end of the cylinder 54, where it acts against the'piston head 58 and moves the piston 55 to the left upon its forward stroke. The piston 55 may be used to operate an injection plunger for injecting molding material into molding dies, which may be clamped by the action of the piston 50, When the piston 55 has reached its forward position, the pressure will be built up in the line l5. This pressure passes through ,t drilled passageway of the valve member 23, into the plunger-lifting chamber 28, where it acts against the annular piston area 30 and lifts the valve member or plunger 23. When this occurs the low pressure constant delivery pump I will discharge its fluid into the line 3|, whence it escapes back into the tank I 0.

To relieve the pressure in the cylinder 54, the operator shifts the second operating valve 60 into the position shown in Figure 1. Under these conditions the line 58 becomes connected to the line 63 leading back to the tank ll, hence, the pressure in the cylinder 54 drops. time the line 65 is connected to the line 61. The plunger of the unloading valve 59 is still raised, however, because the pressure being maintained upon the piston 50 in the cylinder 49 continues to back up through the pilot line 12, into the plunger-lifting chamber II, and to hold the unlcading valve member 13 in its raised position. The low pressure pump I4 is therefore permitted to by-pass freely through the line ii, the relief valve IS, the lines I! and 65, the second operating valve 50, the line 51, the unloading valve 59 and the line 18 leading back to the tank ll. Pressure will also be relieved from the chamber 28.01 the pressure relief valve l5 through its passage 25, thereby permitting its valve plunger 23 to return to its closed position, as is shown in Figure 1.

To cause the piston to return to its retracted position, as shown in Figure 1, the operator now shiftsthe first operating valve 22 into the position shown in Figure 1, whereby there will be a drop in pressure in lines 20 and 12 to. permit the unloading valve plunger 13 to return to its closed position, as is shown in Figure 1. The pressure thereby supplied to the right-hand end of the cylinder 49 and left-hand end of the cylinder 54, causes both piston heads 5| and 56 to be moved in opposite directions awayfrom one another, thereby causing the pistons 50 and 55 to be retracted. When the piston heads 5| and 56 have reached their retracted positions. as shown in Figure 1, the unloading valve 58 will again open, in the manner previously described, thereby unloading the low pressure constant delivery pump IA. The subsequent increase of pressure acts upon the control mechanism of the high pressure variable delivery pump I3, causing its shift ring to be shifted to its neutral position, and thereby shifting the pump itself to a zero delivery ,or neutral position. 'The machine and circuit are now at rest, awaiting the starting of a further operating cycle.

The feature of causing the low pressure constant delivery pump M to by-pass its discharge at substantially zero pressure when the pump delivery is not needed, results in a great reduction of power consumption. The low pressure pump N is the greatest power-consuming unit in the circuit, hence, much power is saved when its discharge is by-passed. The discharge of this low pressure pump 14 is needed only when advancing or retracting the pistons 50 and -55, but as soon as one of these pistons reaches a position of rest, the low pressure pump I4 is immediately unloaded. This unloading of the pump ll occurs when both pistons 50 and ,55 are in their re tracted .positions, as when the hydraulic machine is standing open and idling. It also occurs after the piston 50 has reached its extreme righthand or advanced position. After the piston 55 has reached its extreme left-hand or advanced position, however, the low pressure pump H is not unloaded, but instead, by-passes its dis charge through; the relief valve l5. After the piston 55 is retracted, however, the pump I4 is again unloaded.

Circuit permitting independent retraction of both pistons The circuit shown in Figure 2 permits the retraction of the piston 55 to be made while the Atthesame connected to the common push-back line 45. To

permit this independent. retraction of the piston ferent connections to the right'of the unloading valve 69. The circuit to the left of the unloading valve 69, however, remains substantially the same as in Figure l. The line 46, which formerly led to the cylinder 54, is now severed and leads solely to the port 52 of the cylinder 49. The port 11 of the unloading valve 59 is now connected to the discharge line 18., and the port 58 is connected to a line 8| leading to the lower port 65 of the second operating valve. 60, and thence to the port 53 at the left-hand end of the cylinder 54. The ports BI and 52 remain connected to the discharge line 63, and the port 54 continues to receive pressure fluid from the line 65.

In the circuit of Figure 2 the piston .heads 55 and are again shown on their retraction strokes, and nearing the retracted positions thereof. In the operation of the circuit of Figure 2, as soon as the pistonheads5| and 55 reach the ends of their returnstrokes, the consequent building up of pressure in the system causes pressure to pass through the pilot line 12 and raise the unloading valve plunger 13. in the manner previously described. Additional pressure, howlines l1 and "55, the second operating valve 50,

. 55, the circuit of Figure 2 employs slightly difthe line 8|, the unloading valve chamber and the line 18 leading back to the tank ID.

The pressure fluid coming from the high pressure variable delivery pump |3 causes the check valve l8 to close, as before, and pressure con-- tinues to be built up by the high pressure pump I3. The consequent building up of pressure in the pilot line 12 continues to lift the unloading valve plunger 13, thereby causing a further drop in the pressure line 8|. This action proceed:- until the maximum pressure is reached for which the control arrangement of the high pressure variable delivery pump I3 is set. Assuming this to be 1500, pounds, for the sake of an example,

then a residual pressure of about 200 pounds remains in the line 8| after the maximum bypassing efiect is obtained. In this manner, therefore, while the low pressure constant delivery pump l4 does not by-pass at a zero pressure, it nevertheless lay-passes at a very low pressure which causes the operating motor of the pump |4't'o .consurne very little power.

To advance the plunger 55 the operator reverses the second operating valve 50, thereby connecting the pressure line 65 to the line 58, and connecting the line 63 to the line 8|. When this occurs pressure under the end 82 of the unever, also passes through the line 55, the second 7 operating valve 60, the line 8| and the port l8,-

into the unloading valve 59, where it acts against the lower end 82 of the valveplunger 13. The combined action of the pressure exerted on the annular piston area I4 and the end 82, causes the pressure plunger 13 to be lifted at a relatively low pressure, thereby permitting. the constant delivery pump 4 to begin to by-pass its discharge through the unloading valve 69, into the line 18 and tank H) at a relatively low pressure. In the circuit shown in Figure 2 the constant delivery pump is thus not fully unloaded when the machine is at rest. The actual pressure, however, is only high enough to be barely capable of retracting the piston he'ad'56, hence, may be kept relatively low. At this low pressure the power consumed in driving the low pressure constant delivery pump I4 is relatively insignificant. 7

I To advance the piston 50 the operator reverses the first operating valve 22, as in the case of Figure 1. When this occurs. the fluid passes from the pump pressure lines l9 and 20, through the first operating valve 22 and the line 41, into the left-hand end of the cylinder 49,v causing the piston 50 to move to the right under the combined action of both of the pumps 3 and M. The drop in pressure in lines 20 and 12 when the valve is shifted permits the unloading valve plunger 13 to return to its closed position, as shown in Figure 1. As the pressure is built up in the system, the unloading valve plunger 13 is subjected to pressure from both pumps on both of the areas 14 and 82. This combined action causes the valve plunger 13 to be lifted and the unloading valve 69 to be opened at a loading valve plunger 13 is released through the line 8|, the valve 60 and the line 63 leading to the tank "3, closing the unloading valve 59 so that the low pressure constant delivery pump, I4 is no longer subject to the action of the unloading valve 69 because the pressure in the chamber -1| is now insufficient to maintain the valve plunger 13 raised in its open position. The pressure relief valve l6 now assumes control of the low pressure pump H, the pressure fluid from which causes the piston head 56 and piston to be moved to the left at full pressure. At the end of the forward stroke of the piston 55, the consequent accumulation of pressure in the line l5 passes from the chamber 21 of the pressure relief valve l6, through the drilled passageway 26, into the plunger-lifting chamber 28, where it acts against the annular piston area 30 and lifts the relief valve plunger 23 when a predetermined pressure has been reached. Thenceforth, the lowpressure constant delivery pump I6 is by-passed back to the tank ID by way of the line 3|.

a To reverse the action of the piston 55 and cause it to return to its retracted position, the second operating valve is again shifted into unloading'valve 69 comes into action again to unload the low pressure pump l4 when the of the line l5, the pressure relief valve I16, the

piston head 56 reaches the end of its retraction stroke. Assuming, as previously stated, that a pressure of 1500 pounds'per square inch, for example, is maintained on the piston 50 and applied under these conditions to the plunger-lifting area I4 of the unloading valve 69 by way of the pilot line 12, the valve plunger 13 is nevertheless not lifted.- In order to lift this plunger 13 and open the unloading valve 68, an additional pressure, such as about 200 pounds per square inch, for example, must be also applied through the line 8| and port 68 against the lower end 82 of the unloading valve plunger 13. The pressures stated are purely by way of example, and notcritical.

Whilethe piston 55 is moving backward upon its retraction stroke, the necessary pressure is not built up. When the end of the retraction stroke is reached, however, the additional pressure builds up in the line 8| against the end 82,

until the necessary additional amount is reached,

such as the ZOO-pound pressure previously referred to. The combined action of the pressure from the pilot line 12 upon the annular piston area 14, and from the line 8| upon the plunger end 82, then lifts the valve plunger 13 and causes the low pressure constant delivery pump 14 to be by-passed into the line 18 and tank ill, in the manner previously described. In this way, the low pressure pump I4 is by-epassed at a relatively low pressure when the machine is running idle. With the circuit shown in Figure 2, the piston 55 is operable independently of the piston 50 and can be retracted or advanced at will. In the circuit of Figure 1, however, the piston 55 cannot be retracted independently, but only simultaneously with the piston 50. While, furthermore, in the circuit of Figure 2 the piston 55 is advanced and retracted by only the low pressure pump, according to the circuit of Figure 1, only the advancing stroke of piston 55 is effected by the low pressure pump alone, whereas the retraction stroke of piston 55 is effected by joined action of the low pressure .pump and the high pressure pump. The high pressure pump l3 always unloads or substantially unloads the low pressure pump I4, under the conditions mentioned.

It will be understood that we desire to com prehend within our invention such modifications as come within the scope of the claims.

Having thus fully described our invention, what we claim as new and desire to secure by Letters Patent, is:

1. In a hydraulic machine circuit, a pair of piston and cylinder units, each unit having a piston-advancing area and a piston-retracting area, the piston-retracting areas of both units being connected with each other, a low pressure pump and a high pressure pump connected thereto, means for selectively directing the discharge from said pumps to either the advancing or retracting area of the first unit, means for directing the d scharge of pressure fluid from one only of said pumps to the advancing area only of the second unit tor-advancing the pistons of said units separately and retracting said pistons simultaneously, and means responsive to the attainment of a predetermined pressure in said circuit for by-passing the discharge of said low pressure pump. v

2. In a hydraulic machine circuit, a pair of piston and qylinder units, each unit having a piston-advancing area and a piston-retracting area, thepiston-retracting areas of both units being connected with each other, a low pressure pump and a high pressure pump connected thereto, means for selectively directing the discharge from said pumps to either the advancing or re- 3. In a hydraulic machine circuit, a pair of piston and cylinder units, each unit having a piston-advancing and a piston-retracting area, a low pressure pump, a high pressure pump, means for selectively directing the discharge or pressure fluid from said pumps to either of said areas of the first unit, means for directing the discharge of pressure fluid from the low pressure pump only to the advancing area of the second unit, said second-unit being adapted to be advanced independently of said first unit, means for simultaneously supplying pressure fluid from both pumps to the piston retraction areas of both units, and means responsive to the attainment of a predetermined pressure in said circuit for 1 by-passing the discharge of said low pressure pump.

4. In a hydraulic machine circuit, a pair of piston and cylinder units, each unit having a piston-advancing and a piston-retracting area, a low pressure pump, a high pressure pump, means for directing the discharge of said pumps simultaneously to the retracting areas of both units, means for directing the discharge of said low pressure pump first to the advancing area of the first unit and subsequently to the advancing 'area of the second unit, means responsive to the attainment of a predetermined pressure in said circuit for by-passing the discharge of said low pressure pump.

5. In a hydraulic machine circuit, a pair of piston and cylinder units, each unit having a piston-advancing area and a piston-retracting area, the retracting areas of both units being connected with each other, a low pressure pump, a high pressure pump, means for selectively directing the discharge of pressure'fiuid from said pumps to either of said areas of said first unit,

tracting area of the first unit, means for directsimultaneously, and means responsive to the upbuilding of a predetermined pressure in said circuit behind one only of said pistons for bypassing the discharge of said low pressure pump.

means for directing the discharge of pressure fluid from only one of said pumps to the advancing area of the second unit, and means including a pair of valves responsive to the attainment of a predetermined pressure in said circuit for unloading the discharge of said low pressure pump, one of said valves being adapted to be opened in response to the development of a predetermined pressure by pressure fluid from said low pressure pump only.

6. In a hydraulic machine circuit, a pair of piston and cylinder units, each unit having a piston-advancing area and a piston-retracting I area, the retracting area of both units being connected with each other, a low pressure pump and a high pressure pump, means for selectively directing the discharge of pressure fluid from said pumps to either of said areas of the first unit, means for directing the discharge of pressure fluid from only one of said pumps to the advancing area of the second unit, means including a pair of valves responsive to the attainment of a predetermined pressure in said circuit for unloading the discharge of said low pressure pump, one oi. said valves being adapted to be opened in response to the development of a predetermined pressure by pressure fluid from said high pressure pump onl-g so as to allow unloading of said low pressurexpump at substantially zero pressure thereof.

WALTER ERNST. WARREN R. TUCKER. 

